I know the open differential is welded on for our 335d vehicles. Is it possible to take an existing Quaife LSD on a 335i and put it on our 335d or are both LSD units for either model built differently?

Your problem will be that you will have a significantly higher gear ratio if you swap from a 335i to a 335d. I suppose you could still use every other part of the LSD other than the gear ring, but if you wish to swap out your existing gear ring into the transplant 335i Quaife LSD, you still have to separate the welded ring from your current 335d open differential.

In short, you can't just swap a 335i LSD into your 335d without significantly affecting final drive ratio.

Don't try a 3.46 ring in your 335d. If you think 1st gear is short now, it will be practically useless with a 3.46 ring. Also, I am fairly sure that shift points will not be optimal unless very specific reprogramming is performed.

GBD, I wrote this on the other board, do you think it would be worthwhile to contact Quaife directly? They're in the UK, so there's still time before they are done for the day.

I know you're not addressing me, but why do want to contact Quaife directly? You can call HP Autowerks directly. They are in the US. They can set you up from start to finish. They can answer your questions, too.

Or you can take the advice of another forum member who has already considered changing the final drive ratio (to a lower ratio to make better use of first gear and have a longer gear at highway speed) and considered all of the problems. *cough*

I know you're not addressing me, but why do want to contact Quaife directly? You can call HP Autowerks directly. They are in the US. They can set you up from start to finish. They can answer your questions, too.

Or you can take the advice of another forum member who has already considered changing the final drive ratio (to a lower ratio to make better use of first gear and have a longer gear at highway speed) and considered all of the problems. *cough*

No offense intended, just trying to be helpful to a fellow der. Your plan and comments are much better, however!